Commit 6731d209 authored Feb 04, 2013 by Ilpo Järvinen Committed by David S. Miller Feb 06, 2013

tcp: fix for zero packets_in_flight was too broad



There are transients during normal FRTO procedure during which
the packets_in_flight can go to zero between write_queue state
updates and firing the resulting segments out. As FRTO processing
occurs during that window the check must be more precise to
not match "spuriously" :-). More specificly, e.g., when
packets_in_flight is zero but FLAG_DATA_ACKED is true the problematic
branch that set cwnd into zero would not be taken and new segments
might be sent out later.

Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi>
Tested-by: Eric Dumazet <edumazet@google.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent b6ec447d

net/ipv4/tcp_input.c

+6 −2

Original line number	Diff line number	Diff line
		@@ -3484,8 +3484,7 @@ static bool tcp_process_frto(struct sock *sk, int flag)
		((tp->frto_counter >= 2) && (flag & FLAG_RETRANS_DATA_ACKED)))
		tp->undo_marker = 0;

		if (!before(tp->snd_una, tp->frto_highmark) \|\|
		!tcp_packets_in_flight(tp)) {
		if (!before(tp->snd_una, tp->frto_highmark)) {
		tcp_enter_frto_loss(sk, (tp->frto_counter == 1 ? 2 : 3), flag);
		return true;
		}
		@@ -3505,6 +3504,11 @@ static bool tcp_process_frto(struct sock *sk, int flag)
		}
		} else {
		if (!(flag & FLAG_DATA_ACKED) && (tp->frto_counter == 1)) {
		if (!tcp_packets_in_flight(tp)) {
		tcp_enter_frto_loss(sk, 2, flag);
		return true;
		}

		/* Prevent sending of new data. */
		tp->snd_cwnd = min(tp->snd_cwnd,
		tcp_packets_in_flight(tp));

Admin message